Ultrasound imaging (sonography) uses high-frequency sound waves to view inside the body. Because ultrasound images are captured in real-time, they can also show movement of the body's internal organs as well as blood flowing through the blood vessels. Unlike X-ray imaging, there is no ionizing radiation exposure associated with ultrasound imaging.
Ultrasound devices may be used to perform diagnostic imaging and/or treatment. Ultrasound imaging may be used to see internal soft tissue body structures. Ultrasound imaging may be used to find a source of a disease or to exclude any pathology. Ultrasound devices use sound waves with frequencies which are higher than those audible to humans.
Ultrasonic images are made by sending pulses of ultrasound into tissue using a probe. The sound waves are reflected off the tissue, with different tissues reflecting varying amounts of sound. These reflected sound waves may be recorded and displayed as an image to the operator. The strength (amplitude) of the sound signal and the time it takes for the wave to travel through the body provide information used to produce an image.
Many different types of images can be formed using ultrasound devices. The images can be real-time images. For example, images can be generated that show two-dimensional cross-sections of tissue, blood flow, motion of tissue over time, the location of blood, the presence of specific molecules, the stiffness of tissue, or the anatomy of a three-dimensional region.
In an ultrasound exam, a transducer (probe) is placed directly on the skin or inside a body opening. A thin layer of gel is applied to the skin so that the ultrasound waves are transmitted from the transducer through the gel into the body. The ultrasound image is produced based on the reflection of the waves off of the body structures. The strength (amplitude) of the sound signal and the time it takes for the wave to travel through the body provide the information necessary to produce an image.
Ultrasound imaging is a medical tool that can help a physician evaluate, diagnose and treat medical conditions. Common ultrasound imaging procedures include: Abdominal ultrasound (to visualize abdominal tissues and organs), Bone sonometry (to assess bone fragility), Breast ultrasound (to visualize breast tissue), Doppler fetal heart rate monitors (to listen to the fetal heart beat), Doppler ultrasound (to visualize blood flow through a blood vessel, organs, or other structures), Echocardiogram (to view the heart), Fetal ultrasound (to view the fetus in pregnancy), Ultrasound-guided biopsies (to collect a sample of tissue), Ophthalmic ultrasound (to visualize ocular structures, and Ultrasound-guided needle placement (in blood vessels or other tissues of interest).
Ultrasound imaging has been used for many years and has an excellent safety record. It is based on non-ionizing radiation, so it does not have the same risks as X-rays or other types of imaging systems that use ionizing radiation.
There are various ultrasound procedures that may be used to produce an ultrasound image. The choice of which type of procedure to use depends on the goals for a particular test, the phenomena being investigated and what equipment is available. The most common type of ultrasound picture is a series of flat, two-dimensional cross section images of the scanned tissue. Referred to simply as 2D ultrasound, this mode of scanning is still standard for many diagnostic and obstetric situations after a half-century of use.
In recent years, 2D ultrasound images have also been projected into three-dimensional representations. This is achieved by scanning tissue cross sections at many different angles and reconstructing the data received into a three-dimensional image. A common use for 3D ultrasound pictures is to provide a more complete and realistic image of a developing fetus. By updating 3D ultrasound images in rapid succession, sonographers can also create 4D ultrasound pictures. In the 4D ultrasound, the fourth dimension, time, adds movement and creates the most realistic representation of all.
In some cases, 3D and 4D ultrasound pictures may reveal abnormalities not readily seen using 2D ultrasound. Evaluating blood flow as it moves through blood vessels is a common component of many of the types of ultrasound. While traditional 2D ultrasound and its three-dimensional offshoot show internal tissues and structures, a different kind of ultrasound is required to evaluate blood flow and pressure within a blood vessel.
A Doppler ultrasound analysis bounces high-frequency sound waves off blood cells in motion and records changes in frequency of the sound waves as they echo back to the transducer probe. It then converts this data into a visual representation of how fast and in what direction blood is flowing. A useful diagnostic tool may be preferable in many cases to X-ray angiography because it does not require injecting the patient with contrasting dye.
Three types of Doppler ultrasound are currently in use in addition to routine grayscale imaging. Of these, color Doppler uses a wide choice of colors to visualize blood flow measurements and embed them within a conventional 2D ultrasound of tissues and structures. This provides a more pronounced representation of blood flow speed and direction than is the case with traditional grayscale images. Power Doppler provides color imaging of more sensitive and detailed blood flow measurements than regular color Doppler does. It can sometimes even achieve images in situations not accessible with color Doppler. However, power Doppler is limited in another way because it cannot indicate the direction in which blood is flowing. Like conventional and color Doppler, spectral Doppler can scan to determine both blood flow and direction but displays this data in graphic form rather than with grayscale or color images.
It is known to use a function generator for generating ultrasound frequency pulses. The basic function generator is usually a piece of electronic equipment or software used to generate different types of electrical waveforms over a wide range of frequencies. More advanced function generators, such as arbitrary waveform generators (AWG), use direct digital synthesis (DDS) techniques to generate any waveform that can be described by a table of amplitudes. Direct digital synthesis (DDS) is a method employed by frequency synthesizers used for creating arbitrary waveforms from a single, fixed-frequency reference clock. DDS is used in applications such as signal generation, local oscillators in communication systems, function generators, mixers, modulators, sound synthesizers and as part of a digital phase-locked loop.
The equipment and software currently required for generating a sequence of pulses have limitations of being complex and costly. Thus, it is desirable to provide a better solution in order to overcome limitations of the existing technologies.